Method and apparatus for producing sound waves



Mart-Bh 7, 1933. A M TEWKSBURY 1,900,623

METHOD AND APPARATUS FOR PRODUCING SOUND WAVES Filed Dec. 17, 1931 4 Sheets-Sheet l March 7, 1933. A M TEWKSBURY 1,900,623

METHOD AND APPARATUS FOR PRODUCING SOUND WAVES Filed Dec.` 17, 1951 4 Sheets-Sheet 2 Mm Meu/mary g @m9 v v www March 7, 1933. A M, TEWKSBURY 1,999,623

METHOD AND APPARATUS FOR PRODUOING SOUND WAVES Filed D60. 17, 1931 4 SheetS-Shee't 3 arch 7, 1933. A M TEWKSBURY 1,900,623

METHOD AND APPARATUS FOR PRODUCING SOUND WAVES Filed Deo. 17, 1951 4 Sheets-Sheet 4 ALLEN M. TEWKSBURY,A 0F.

Patented Mar. 7, i933 METHon'AND Preserve rentra-opnemesoUND'WAvEs j Application filed December l?, 1931. 'SeralNm 581,555.

This invention relates to'newand useful improvements in a method and 'apparatus for producing sound waves.- f Y rlfhe primary object of this inventionis to vprovide a new method of producing sound waves, and apparatus-forcarrying out this method.

A further important objectroft e invention is to provide'means lfor producing Vsound waves of super-volume which Vis especially adapted feruseyin public address systems, although not limited to this type ofl use.

A Jfurther object of the invention is to provide nieansfor producing sound waves, which means is capable ofuse as a loud speaker in connection Awith radio receiving sets.` In this particular use, the device is'adapted to relieve the delicate voicecurrents of the work of movinglarge members, such as Ycones or diaphragms, aswell as large volumes of air to form sound waves, as 1s required 1n most present day loud speaker units.

f-L further object of the invention to provide a device which is capable'ot increasing the eliiciency of loud speaker units.

' Still another object( of Y.the 4invention isto provide a'device capable of taking full ad;v

vantage of the push-'pull operation of vacuum Y tube ampliiers."

Still another object 'of the invention is to provide a device capable of producing sound Waves of a volume limitedentirely by the capacity of the device to mechanically produce sources of fluid'maintained atpressures above and below atmospheric pressure.VV Y

YAnother object of the invention is to provide ra device capable Voi! producing sound waves or' any desired volumehaving very low frequencies. j

@ther objects and advantages of 'theinvention will become apparent during `the course of the following description.

f In the accompanying drawings forming a part of this specic'ation, and in which like numerals are employed to designate like parts throughout the samej:

Figure 1 is a top-plan viewv of thedevice embodying this invention', f i Y Figure 2 isa front elevational'view of the Vdevice illustrated in, Fig; 1, u Y

l end Vportion ofth'eplate is a cylinder l2.

Vview taken on line S-.Sof Figi, ,y

Figure t is a fragmentary -horizontalsectional view taken'on linee-44 of Fig.- 3, f v

Figure 5 is a vertical sectionalpviewtaken on line 5-,5 of Fig. 3,1; 1 Y e VFigure 6 is a verticalsectio'nal view taken on line 6 6 of Fig. 3, L v

Vligure 7 is a verticalsectional view taken online 7 7 of Fig. 3,A and ,i e o 1 60 igures 8 and 9 represent two 4sines'of simple air waves which have been shadedto compare the relative expenditures of energy intwo dierent typesfoffsound waveproducing'devices. .L ,1. riellyrdescribed, this invention consists of apparatus capable.ofimechanicallyproducing kapush-pull movement of theair colf umn in a horn or other .similar sound distributing device with the mechanicallyy `pro- Y 70 duced' push-pull action controlled electrical- 1;. ly'. The device consists of a source ofluid y maintained at a pressure above atmospheric pressure', and confined; within the pressure reservoirv ,Af and the: pressure- .working cylin-V der Band a sourceof fluid maintainedat a 'i v pressure below atmospheric pressure' and cong nedVVV within` a pressure reservoir. (l1-and. a, working cylinder D; Ihesesources olfrfluidmaintained under pressurefand vacuumrareso controlled by a'va-lvennit-"E.which estab# lishes and 1destroys connection 1 between these two sources and a' horn lor theli'ke, F; The

movable element otthe'valve unit E is actuated in this particular l"illustrationofthe in'- vention, by a Dynamic voice fcoil unitG.

VThe'V independent source of Vpressure yand vacuum' are alternately connected with the; horn F, at an'audio frequency, in proportion-Y to the variations in. amplitude and frequency 9 of a controlling electrical current, such asia voice current. 'l 3* f 1 For-thepurpose of enabling.thosegskilledll inthe art towarrive yata completeunder-V standing of Vthe features''oi' the construction, 9 thefdevi'ceiwill now be described indetail. Al suitable base or .supporting surface lgis provided, and Yhas" suitablysecured thereto) a mounting plate l1.V Positioned; uponone 'stitutesthe pressure reservoir A in which fluid, such as air, is stored under'a pressure above atmospheric pressure. This fluid is stored in this Vreservoir forthe purpose of maintaining the same at a uniform pressure, and is supplied thereto from a prestsure pump, `ofthe like,not'shown,`through the conduit 1-5. The fluid under pressure vconfined within the reservoir A is conveyed to the pressure working cylinder B by means fof Ja conduit 16.

The opposite end portion of the plate l1 fhas positioned thereupon `a second cylinder 17,r which is closed atfitslower end by the plate 11 and at its upper-end by the plate 18. Tie rods 19 are employed to connect these V.various elements'which cooperate with each other to formthe reservoir C which constitu'tesia source offluid maintained under pressure "below latmospheric pressure,` or maintained at a vacuum. j This vacuum reservoir C is connected to a suitable vacuum pump, not shown, bymeans lof a conduit 19', and is connected toa vacuum working cylinder D byl meansfof a'cond'uit' 20.

The outer end'oflthe pressure working cylin'derjB 'is supported by means of an end plate 21 connectedto :a mounting` block 22 which,

isinl'turn secured tothe end plate or head V13 ofthepressure `reservoir A. .Thewouter end 'of `the'vacuum 'working cylinder DV is secured to Vthehead 18ofthe vacuum reser-` voir C by means of an end 4plate 423 secured to a supporting block 24, which in lturnis connected to itherhead I8. `These working VcylindersB'and Dare arranged substantially in axial alignment with `respect to each other,

and have their inner ends connected respectively to end plates25 `and 26 bymeans of tie rods27and28. Thesetie rods pass through the enclplates-21 and23,and are threaded at their rinner yendsinto apertures formed in thepla'tes 25 and26. These Yplates 25 and 26 are relatively'adjustably tied together by screws'29,'which-are associated with `the Various corners ofthe said plates. `F or the purpose of maintaining these-plates 25and 26 in proper spaced relation with respect to each other, 'the plate '25 fhas "formed therein four elongatedapertures 30, capable of receiving pins 31` projecting =from the spacing blocks 32. These spacing `blocks are secured to the plate 26 by means of screws Adjusting screws B4arefassociated with the elongated apertures SOfand .project into `the samein the 'directions of their maj or dimensions. It

will be seen that by loosening the various screws 29 and adjusting the various screws 34, the two plates 25 and 26 may be shifted relative to each other in parallel vertical planes.

For the purpose of sealing the space between the-two plates `25 and 26, and yet permit relative adjustment between the same, these plates have secured to their inner faces channeled lst-rips A. strip oristrips 36 of v flexible material, such as cork, are positioned with their opposite edges seated in the channels ofthe members 35. The strip or strips 36 terminate at relatively spaced ends 87 to form a lateral opening between the plates 25 :and :26. This opening registers with the bore `of a lhorn or :the like, 38. It will be seen that the space between the plates 25 and 26 forms :a sound chamber 39 which communicates "with the horn 38. e

"lhis-sounclichamber 39 also acts as a valve chamber 'for housing the valve 40,` This valve is formed of two parallel plates 41 and 42. These plates are heldin spaced relation with respect to-each other by ,spacing blocks atthe opposite ends thereof, Vwhich leave thesides open. Communication, therefore, Aisiestablishedbetween theinterior 44 of the valveV unitandthe sound chamber-.39. Each valve plate A41 vor 42 is provided with a pluralityof'transversely extending elongated slots Y45 andthe slots in the respective valve plates-arefarranged lin transverse alignment. This valve :unit V41 is adapted for move nient withinthe sound chamber 39 and is intended to partake of slight oscillatory movement in a vertical direction.-

`For the .purpose oflsupporting this unit 4l `to permit ofthis movement, a pair of parallel springimembers 46 areconnected at their inner ends tothe 'spacing blocks`43, and are connected attheir outer ends to a support 47 which islsuitably positioned between andsecured to one of the plates 25 and 2G. Y

The saidplates'25 and26 are each formed with a pluralityof slots 48, and the slots of of the plate 26. The slots 45, formed in the i valve unitv 40, and the slots 48 formed in the end plates.25 and 26 Aare of equal size, with the result that when the valve unit 40 is positioned 'with the slots 45 4in the plate`41 registering `with 1the slots 48 in the end plate 25, communication will be established between the pressure `working cylinder B and the sound chamber 89. 'Lila'.ewise,l when the slots 45 in the valve plate 42 regist`er with the slots 48 in the end plate 26, thevaeuum working cylinder 'Dwvill be `in communication with the sound chamber 39. It will be noted, however.y `that `due "to the staggered relation of the slots'48 in the :respective plates 25 and 26, both of the werking cylinders BandA 'b can never be connected at one time to the lsound chamber 39. f

housings 52. Positioned within each hous-v ing is sliding block 53, and the inner ends 'of the spring members 49 are connected to these blocks. rEach block is formed with an internally threaded aperture 54 which receives av threaded end of'an adjusting rod 56. Theseguide housings 52 are open at their inner ends and have the various edges of these innerendsjsecured by braZing, welding, or

fthe like, to the face of the plate 26. It is to be understood that any other suitable form of connection may be provided .between these housings 52 and theend plate 26,and that-if necessary,lpacking material maybe located between the housingsandy the end plate. j e The outerends'of ythezadjusting rods-'56 pass through the end plate- 21 and the end wall 57 of the pressure working, cylinder B.

The'eXtremities of these rods are provided with screw-driver slots 58 by means of which lthe-rods maybe rotated. Wvashers, or other suitable stop elements 59 and 60 are connected to the yrods 56 to prevent aXial Amovement of the same in either direction. -f

vThe valve unit y must be permitted to freely move with respect to the endfplates 25 and without'binding or frictionallyr engagingthe same. For this purpose, the y.spacing .i blocksk 32, employed for maintainingthe "'40 plates-25 and 26 inY proper spaced vrelation with respect to eachother, arema'chined to hold the plates 25 and -26 sufficiently spaced to enable the'valve unit to slide relative -to the same. The spacing between the valve y unit and the respective end plates 25' and 26, as illustrated in Figs. 3an`d 4, is exaggerated to better'enable the features of construction ofthe valve unit to be clearly illustrated.Y It

, is to be understood that the valve plates 4l 'I and42 of the valve unit are positioned suf- {ici'entlyclose to the inner faces of the end plates 25 and 26 to prevent leakage between Y these opposing surfaces.` 'it will be noted that of fluid upon the;V valve unit.i

the' end plates 25 and 26 really function as valve seats for the respective valve plates 4l and42. By adjusting the rods 56,' the valve unitmay be shifted transversely with respect tothe valve seats or pl`ates25 and 26 for properly positioning the valve unit with respect to the valve seats.`V The springconnections 49, between vthe valve unit andthe-adj ustable blocks 53, valso function tobalance'forr counteract the actions of the two different 'sources F or the' purpose of actuating vthevalvein' These blades extendv timed relationwith variations in amplitude Y Y and frequency ofa ycontrolling current, the valve-unitis connected toa rod 6l through the mediumv of al flexible blade-like portion 62'.y This rod 6l is connectedto the movableLY -coilr 63 of the Dynamic voicepcoil unit Gr. ft is not intended tospecically describethe Y Adetailed features of construction yof'this unit Gr, as any suitable Dynamic unit maybe employed.-r It is further to be understoodf.

that other suitable means may be utilizedfor causing desired reciprocation of the valve s `unit40. In connection with the Dynamic unit 26, it is suflicient to say that-thefvoice`A coil 63 isconnected bythe conical element y 64 and the rods 65 to the valve rod 6l, and vthat the movable coil l 63 -is supportedbyV a flexible membrane 66, AVwhich in turn: is

'mounted upon the 'outer pole pi'ece67Y of thev A DYMUHC unit'G. This unit a-lsoincludes an inner polev piece68` and a coil-;69` Itis to'be understood that the movable voice-coil 63 is 'suitably connected lto an! amplifying unit or a radioreceiving unit, and that the vcoil A69 is vsuitably connected toy an'.v external sourceof electricity, as is customary with dynamicV units of Vthis generaktypeJfThe unit G is suitably supported upon the base plate 1l by means of legs or blocksZO, and

is tied to this base plate by means ofthe rods 7l connected to the housing of the coil: 69

by means of blocks 72.

Y The mode of operation of this device be described as follows:-V`

The pressure reservoirA land the vacuum reservoir@ are to-be connectedto suitable sourcesof pressure and vacuum Vby means of the conduits l5 and? 19.Y The vworking cylinders B and D respectively areconstantly 1n communication :with the' reservoirs A im and C, and fluid will be maintained in these Y and 'vacuuinfrespectively Y When the voice coil 63 is caused to'move dueto the ordinary operation vof an' amplifying unit or radio receiving set connected ylinders B, and VD under :pressurev to the same, the Yvalve unit'40 .isL caused to Y reciprocate within the sound chamber :39for alternately establishing communication `between the pressure working cylinder YB- and the'sound chamber r39.- and the vacuumworking cylinder D- andfsaid sound chamber.

"WhenA the pressure vworking cylinderV B is placedY in communication with `the sound vchamber 39, the air column in the horn38is pushed outwardly of ythe horn.YV When the vacuum working cylinder D is placed'incoinmunication with the sound' chamber `39, the

air column in the horn 38 is pulled inwardly.

This alternate establishing of connections between the horn 38 and the cylinders B and to produce-sound waves It wilhbeilnoted D, produces the desired pusli-pull action-`r v within the horn l38or'causes theair'fc'olumn 'in the horn to'move outwardly andinwa'rdly Y Y tl1atrthe-orce of this push-pull action upon it-hear columnlin the horn is dependent soleily upon the degrees of pressure land vacuum imaintained in the cylinders A, andC, and .thatvthc volume of sound producedby this device, therefore, is substantially unlimited.

EI am aware of the Jfact that sound Wavev :producing devices have been designed which employ either pressure or vacuum. To the Y ibest` of my knowledgek and belief, my device `istheqhrst one to use both pressure `and vactuum. WVhen the `pressure or vacuum alone is .used,there is a material Waste of energy.v :With `my device, there is no Waste, as energy ,isfonly being.v expended when the device s .'beingvmodulated. `Figure 8 illustrates ak ,simple sine Wave of a sound which has been shaded to representjthe expenditure` of enrergy and the absence of Waste With my par zoticula-r device. Figure 9 represents `a simplesine Wave of ar 'sound shadedv to represent `the expenditure of `energy to produce the sound andthe loss of energy in the prior art type of device.

P :Referring to F ig. 8, it Will be ,seen thata usound Wave mustv start from some neutral point, which, in this case, is represented by the line X. The pressure part of the Wave .originatesat O on line'X, increases in amplitude .until Vit reaches the point C,'where it begins to fall ofi' until it reaches the neun tral line X at the pointE; ,Atthis point, `the Wave begins'to `enter the vacuum region and continues down to, the point D, which `in `a pure sound Wave, Will be as far belovvlthe lineas point C is abovethe line. ln `my device, this` condition isexactly duplicated, ybecause at the instant an impulse is communicated -to the valve, all'ports are 40 closed, and no energy isbeing consumed, this representing the neutral line X. As the valve unit 40 begins to open, because of this impulse, pressure will be released through the valve and will cause a risein pressure `in the `horn. This pressure will continue to rise as the valve continues to open, until itreaches the point as at C, when the valve Will begin to close and cause the pressure ito drop until the valve reaches its centralized or normal position. The pressure Will ,then be represented ,by the neutral orwzeroline at the point E. As the valve is following the VWave form of `the current which is moving it, it will continue past the 155 neutral-line X, and vacuum Will be released causing a drop ot pressure or a vacuum in the horn. The valve will continue to open and cause the pressure to continue to drop until `point D is reached, when it again begins to `close to the vacuum and `allow the pressure to again reach the neutral or Zero line l y t It Willibe seen :Erom'theabove that when my device `is notbeingexcited or modulated, L the .valve ports will be closed to ,both vacuum rand pressure; therefore no ,expenditure of energy occ-urs. y It Will further be notedthat there will ,actually be created pressure and Ivacuum in thehorn, and that each reversal ,of ,fthevalve there' will be a like reversal ,through the horn, the vave form resulting from this action vvill` exactly Acoincide With the Wave form ,Which causes the valve tomove.

ln devices using pressure orvvacuum alone, an entirely different condition exists as to Wave form and as to efficiency. In referring to Figure 9, it will be seen that in such .a device, the Wave form must .start at some point above or belovs the neutral yor zero line, as

at O, which at once disclosesthe fact that in l,

using eitherv pressure or vacuum alone, the valve, when in its neutral position, mhst be open, and allovv escape of .energy `Itmust be open to such an` extent thatwhen handling :sounds oi its greatest amplitude, it Willnever entirely close orvcrossthe neutral line. If this does occur, it is evdentthere will bea latplaee on the Wave as at line Z, Y, which `means distortion.v It will also be seen that must be a constant Waste of energy. Any attempt to increase its volume Will result 'in a.` greater Waste of energy.

,The shaded portionsof Figs. 8 and 9 represent expended energy. f

The line M in F ig. 8 is intended to repref sent the consumption of energy in my device,

yor the absenceof consumption ofrenergy,

when the valve is centralized or `vvhendthe device is not being modulated. The shaded space designated by the character N in Fien 9 is Vintended to represent the consumption of `energy in a. device of the prior art, or a device using either vacuum or pressure alone when such 'a device is not being modulated. The aircolumn ina hornassociated with a device using eitherpressure or vacuum alone will `alvvays be moving inthe same direction,l and `Willnever be completely stopped and never reversed. A soundwave thuscreated will not have the `same form as the-.Wave eX- isting in the current controlling the valve, and, therefore, there Will not be .an exact duplication of this controlling Wave.

It Will be evident from a study of the sines shown in Figs. 8 and 9, that a device using either pressure or vacuum alone will consume the sameamount of energy When not being modulated or excited as when it is being modulated `to its fullcapacity. In my device, the imput energy is in direct proportion` to the output energy, and no loss occurs when the device is not being modulated or excited.

It is to be understood that the form of this invention herewith shown and described is to be taken as a preferred example of the same, and that various changes `in the shape, size and arrangement of parts maybe `resorted to Without departing `ijromthe spirit ofthe in using one of these prior art devicesthere invention or the scope ofthe Vsubjoined claims.

Having time described, the eventim, i"-

claim l'.V Ina device for producing sound waves,

a soundY chamber, af's'ourcei oi pressure,v a`

source of vacuum, and Ameans for successive- 1y connecting said separate'sources with said chamber. f

1 2. In a device for producing sound waves, asound chamber, a source of pressure, a

source of vacuum, means for controllingcoin.

munication between said separate sources and said chamber, and means 4for yactuating said' first mentioned means.

3. In a `device for producing sound waves, a-so'und chamber, a source 'of pressure,.a source of vacuum, a valve for controlling communication between saidseparate sourcesy andsaid sound chamber, andmeans for actuatingvsaid first mentionedy means. l c

chamber normally containing a column of 5W neans for causing the said column of air to 4. In a 'device for producing sound waves, a soundcharnbeij afsource ofv pressure, Va

sourcefof vacuum, a valve for controlling eommunicatioiibetween saidseparate sources and said soundchamber, and electro-mag netic means for actuatingsaid first mentioned means; v j c Y.

5. In a device for producing sound waves, a sound chamber, a source of pressure, a source of vacuum, a valve forv successively connectingsaid lseparatesources with said chamber, and electro-magnetic means forV actuatingsaid valve'. n

6.Y In a device for producing sound waves, a sound chamber, vand fluid means for causing movement of the airin said chamber in opposite directions at audible frequencies.`

7; In a device for producing sound waves, a

air atatmospheric pressure, a source of fluid maintainedl at a pressure above atmospheric pressure, a second source of iiiiid maintained at a pressure below atmospheric pressure, and

and frequency of' acontrolling-voice current.

9. A vmethod of 'producing sound waves comprising maintaining a body-.of fluid at a pressure.V above atmospheric pressure, maintaining a second body of Huid at a pressurebelow atmospheric pressure, and subjecting an air column alternately tion of said bodiesfof fluid.

104A method for producing sound waves comprising maintaining a body of fluid at al pressure above atmospheric pressure, maintaining a second bodyof fluid at a pressure below atmospheric pressure,and connecting at an audio frequency., an air column. alter nately tothe separate actions of said bodies Y of fluid. y

1l. .A method lforiproducing sound waves comprising maintaining a .body of iiuidatf a pressure above atmospheric pressure, main-j taining a second body of fluid at a pressure below atmospheric pressure, and subjecting the air column alternately and to aj variable to theseparate arc-'k extentto the separate actions -of'said bodies l g 12. A method foipr'oducing sound waves comprising.v maintaining a body'of fluid ata pressure above atmospheric pressure, 'mains taining y'second body of* fiuidv ata pressure below Vatmospheric pressure, and subjecting', an air column-alternately lto the separate ac`.

tions of said bodies of `iiuid inproportioii to the lvariations in amplitudeand frequency of a controlling voice current.,

13. A 'device for producing soundwavesl comprising a pair of 'substantially aligned" cylinders, means for maintainingfluid under pressure in one of said-cylinders, meansfpor maintainingiiuid undei1 vacuum in the second Y of said lcylindervsaahorn, and means foifal Y ternately connecting the said cylinders the interior of said horn.' f c 14. A device fonfproducing sound wavesV comprising a pair of'cylinders arranged inf end to end relation, a valve chamber located between saidcylinders, said cylinders havingy openings vestablishing fcom'inuiiicationi be'w`` tween the same Vand said .valve chamber, means for maintaining -fluid `under'y different degrees of pressure in saidcylinders, av'alve Y y in the valve chamber, and means; for actuating Y the valve to independently open and close 'the openings in said cylinders.

' 15. A device for producing sound waves comprising apair of cylinders arranged'in end to end relatiOm'means for maintaining fluid under :uniform v pressure above at1nos. pheric pressure in one of said cylinders, means for maintaining a. fluid underuniform ,pres-j sure below atmospheric pressurein the second of said cylinders, afvalve lchamber communieatingr with both of said cylinders,- a valve for controlling the communication between said valve chamber and said cylinders, and means'v for actuating said valve Vin response to variations in amplitude and frequency of a controlling voice' current.

j 16.' In a device forproducing sound waves,.. a sound chamber, fluid means for causing movement of. the air in said chamber i`n1op- Y positeV directions, and means for'rvalving the *5130 action of the fluid means.

17. In a device for producing sound Waves, a sound chamber, fluid means for causing movement of the air 1n said chamber f1n 0pposite directions, means for producing a mag- 5 ietic field, and means under the influence of the last mentioned means for controlling the fluid` means.V

18. In a device for producing sound waves,

'5J a sound chamber, fluid means for causing novement of the air in said chamber in opposite directions, means for producing a constant magnetic field,`means for varying the constant magnetic lield, and means influenced gz by the resultant varying field for controlling 15 che action of the fluid means.

19. In a device fgr producing sound waves, a sound chamber, fluid means for causmg movement of the air 1n said chamber 1n opc. posite directions, means for producing a con- :tant magnetic field, means for varying the constant magneticfield, and means influenced by the resultant varying field for modulating the moving air in saidrchambelr in accordance if; with the varying resultant field.

f2.0.V In a `device for producing sound Waves which employs compressed and rarilied air as the sound wave producing medium, means for producing a varying magnetic field, and

2; means influenced Aby said field for controlling he action of said compressed and rariiied air. 21. In a device for producing sound waves which employs compressed and rarified air as the sound vwave producing medium, means for 'in valving said air, andk electromagnetic means magnetic means operated by telephonie cur-` rents for controlling the movable part of said .'al've. i

23. In a. method of producing sound waves comprising creating a body of compressed air, creating a body of rarified air, producing I a. varying magnetic field, and causing movenient of a column of air byisubjecting `the same to the actions of said bodies o'tair in accordance with `the variations of, said field.

2L In a device for producing sound Waves,

555-51. sound chamber, a'sourceof pressure, a source of vacuum, and `:mean-s for connecting said separate sources with said chamber.

25. In a Vdevice for 'producing sound Waves,

a column of air, a source of compressed air, a

6o "ource of rarefied air, and means for employ.

ing said compressed and rarefied air for causingr movement :of the column of air.

26. In a device i'or producing sound waves, a "sound chamber, a source of pressure, a source 65 of vacuum, and valve means for `controlling communication betweensaid separate sources and said chamber. v Y Y f 27. In a device for producing sound waves, a sound chamber, a source of pressure, a source (ivacuum, means for controlling communication between said separate sources and said sound chamber, `and electrical means"` for actuating said first mentioned means.

28. A method .ofvproducing sound waves comprising maintaining a body of fluid at a pressure above atmospheric pressure, maintaining a second bodyof fluidat a pressure below atmospheric pressure, and subjecting an air column to the action of said bodies of Huid. v Y

29. 1A `method of producinglsound waves comprising maintaining a body of, fluidat a pressure above `"atmospheric pressure, maintaining a second body of fluid at a pressurelbelow atmospheric pressure, and sub` jecting at an audiofrequency an air column to the actions of said bodies of fluid'.

30. A method for producing sound waves comprising maintaining a. body of iiuid at a pressure above atmospheric pressure, maintaining a second body of fluid at a pressure below atmospheric pressure, and subjecting an air column to a variable extent to the actions ct saidbodies of Huid.

3l. A method' for producing sound waves comprising maintaining a body of fluid at a pressure above atmospheric pressure, maintaining a second body of fluid ata pressure below atmospheric pressure, and subjecting an air column to the actions of said bodies of fluid in proportionkto thevariations in aniplitude and frequency of a controllingmvoice current. a 'v 32. In a device for producing sound waves, a column of air, fluid means for causing movement of the air in said column in opposite directions, and means for modulating the moving air. Y

In a device for producing sound Waves, a column of air, a valve, two separate sources of air maintained at different pressures and adapted, under the control of said valve, t0 cause movement of the air column to produce sound waves, means for balancing the valve against the actions of said. sources of air, and means for controlling said valve.

34. In a device for producing sound Waves, a column of air, a slidably movable valve, two oppositely positioned sources of air maintained at diii'erent pressures and adapt ed, under the control of said valve, to cause movement of the air column to produce sound waves. meansV supporting and balancing the valve against the actions of said sources of air, and means for controlling said valve.

S5. In a device for. producing sound waves, a column'of air, a source of `compressed air, a source 'of rarelied air, and means for controlling communication between said column lic 1,900,623l v '7'l and' sources so lthat the column can be affected by one source only at any one time.

' 36. A method of producing sound Waves comprising subjecting a body ofair to the independent actions of different air pressures capable of moving said 'aircolumn in differentl directions, and modulating the moving air. l

In testimony whereof I aix my signature.

ALLEN M. TEWKSBURY. 

